Can I copy a module from an old project into a new crate and it will always work without adjustments?

What about code examples from StackOverflow, or Github issues? Will these work without adjustments in my local project?

Will a future syntax highlighter always be able to highlight the code in my old Rust articles?

Will future tooling always be able to read my current code?

Can I make editor macros and snippets that will keep working in every version of Rust?

If I can write code in one crate and it will compile, but then write it again in another, newer crate and it doesn't, then it isn't backwards compatible. Plus, as noted above, "code will keep compiling" isn't even a guarantee that the language team gives you.